There are presently in use on rapid transit type railway vehicles both fluid pressure and electrical types of trip cock devices, one type being used independently of the other. When the fluid pressure type trip cock is tripped by a trip arm located strategically at some point along the track, valve means in the trip cock is opened to cause reduction of brake pipe pressure at an emergency rate for effecting an emergency brake application on the train and at the same time cause release of fluid pressure acting on a pressure operable electric switch which is thus operated for effecting energization of control means for causing propulsion power to be cut off. When the electrical type trip cock is employed, tripping of the trip cock causes an electrical switch therein to be operated to a position in which a control switch is actuated for energizing a train wire circuit. When the train wire circuit is energized, propulsion power is cut off concurrently with operation of brake control device on all the cars for effecting an emergency brake application thereon. In either case, whether it be the fluid pressure type or the electrical type trip cock, if the trip cock on the lead car, for example, fails to function properly, the amount of additional travel of the train, due to such malfunctioning of the trip cock, before it is brought to a stop may be critical. By the time the trip cock on the following car has been actuated, the lead car may already have traveled into the path of travel of another train approaching on an intersecting track.
Trip cock devices are also employed as back up means to assure stopping of a train such as, for example, when the train is entering a track section on which a disabled train is present, or when the train enters a depot, in which case the train will automatically be brought to a stop in the event the operator fails to do so.